Mechanical tensioner struts are used to absorb or dampen force applied to the strut in a first direction by displacing a first component, to which the force is applied, in the first direction with respect to a fixed component of the strut. For example, struts are used to modulate force and vibration associated with operation of chain systems. A spring for the strut opposes the displacement of the first component in the first direction and the degree of displacement of the first component is a function of the relative magnitude of the applied force with respect to the spring force. Upon release or reduction of the force, the spring displaces the first component in a second direction, opposite the first direction, with respect to the fixed component. It is desirable to eliminate or minimize dampening of the first component in the second direction. That is, ideally, the dampening of the strut is uni-directional only in the first direction.
To maximize dampening in the first direction, frictional forces generated by contact of the first component with other components of the strut are maximized. However, maximizing these frictional forces maximizes forces which lock the first component in a contracted position (displaced a maximum distance in the first direction). If these forces are too great, the spring is unable to displace the first component in the second direction when the force in the first direction is reduced or removed. Further, even if the spring is able to displace the first component in the second direction when the force in the first direction is reduced or removed, the frictional forces may still be present during the displacement in the second direction, resulting in undesirable dampening in the second direction.
U.S. Pat. Nos. 6,702,266; 6,612,408; 5,951,423; and 4,606,442 as well as U.S. Patent Application Publication No. 2002/0025869 disclose the use of complementarily angled and mating respective surfaces for components engaged during operations to dampen a force applied in a first direction. Decreasing the complementary angles increases desired dampening. However, to prevent the surfaces from locking together (due to frictional and compressive forces), which would prevent desired displacement in a second opposite direction when the force is reduced or removed, or would result in undesirable dampening in the second direction, the angles must be kept relatively large. That is, if the angles are too small, the engagement of the respective surfaces results in such a large frictional/compressive force holding the respective surfaces in contact that the surfaces remain locked or at least partially engaged when the force is reduced or removed. Thus, the range of operation of the respective devices is undesirably restricted and/or undesired dampening in the second direction occurs.